The perinucleolar compartment (PNC) is a unique nuclear structure whose formation is correlated with the malignant phenotype both in cultured cells and in human cancer. Our long term objective is to understand the function of the PNC and its significance in the development and maintenance of the malignant phenotype. We will begin by addressing three problems. 1) What are the functional events that take place in the PNC? We have recently shown that the PNC incorporates labeled nucleotides within a short period of time, suggesting its involvement in RNA metabolism. We will clarify whether the incorporation represents transcription, or the post-transcriptional modification of RNA, or a combination of both, by analyzing the sequences where the labeled nucleotides are inserted, by determining whether the PNC is associated with chromosome and/or specific genes, and by examining the presence of transcription factors and RNA processing factors in the PNC. 2) What are the mechanisms that induce the formation of the PNC? We have found that the integrity of the PNC is influenced by the transcriptional state of the cells. We will experimentally change the level of rRNA and/or some of the pol III gene expression, and thereby examine the potential coordination between the activities of the two polymerases and their effect on the prevalence of the PNC. 3) What are the molecular constituents of the PNC? We will isolate and identify additional proteins and RNAs that are part of the PNC, thus generating more information with which we will search for factors that are responsible for the formation of the PNC and its function. The results of these experiments will provide an important foundation to address the significance of the PNC in malignant cells.